Microlithography is used to produce microstructured components, such as, for example, integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus, which has an illumination device and a projection lens. The image of a mask (=reticle) illuminated by means of the illumination device is in this case projected by means of the projection lens onto a substrate (for example, a silicon wafer) coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask structure to the light-sensitive coating of the substrate.
In a projection exposure apparatus designed for EUV (that is, for electromagnetic radiation having a wavelength of less than 15 nm), owing to light-transmissive materials not being present, mirrors are used as optical components for the imaging process. The mirrors can be fixed on a carrier frame and can be configured such that they are at least partly manipulatable, in order to enable a movement of the respective mirror in, for example, six degrees of freedom (that is, with regard to displacements in the three spatial directions x, y and z, and also with regard to rotations Rx, Ry and Rz about the corresponding axes), as a result of which it is possible to compensate for changes in the optical properties that occur for instance during the operation of the projection exposure apparatus, for example, on account of thermal influences.
During the operation of EUV systems, dynamical aspects are of increasing importance, for instance when suppressing parasitic forces on the respective elements or when taking account of and suppressing vibrations excited by the system. To this end, a contributing factor is, inter alia, that the natural frequency spectra of the mechanical structures shift ever further to lower frequencies for the growing dimensions of the mirrors and of the support and measurement structures, which dimensions increase with numerical aperture. As a result, vibrations that occur lead to growing problems in respect of the system performance and also in respect of the fact that active position regulation can no longer be operated in a stable manner or only with low control quality.
The prior art has disclosed various approaches for suppressing or damping unwanted vibrations. To this end, reference is made in an exemplary manner to U.S. Pat. No. 7,826,155, WO 2007/006577 A1, DE 10 2008 041 310 A1, United States patent application publication 2012/0138401 and U.S. Pat. No. 4,123,675.